Currently, the most accepted method of metering fuel to internal combustion engines is through the use of pulse-width-modulated (PWM) solenoid valves referred to as fuel injectors. For these engines, a microprocessor provides control signals of the proper timing and duration for proper fuel delivery by the fuel injectors. For conventional engines that use liquid fuels, such as gasoline, fuel injectors are oriented with one end protruding into an intake port near the combustion chamber intake valve. The other fuel injector end receives fuel from a manifolding device. This placement of injectors, one per intake port, is commonly referred to as multipoint injection.
Multipoint fuel injection of alternative fuels is a highly attractive method of metering fuel. Multipoint fuel injection, for example, permits much more precise control of fuel flow than do single point or conventional introduction systems. This is particularly important for gaseous fuel engines. Conventional multipoint fuel injection systems, however, do not easily permit either dedicated multipoint alternative fuel injection or bi-fuel multipoint system operation. Most existing alternative fuel systems for gaseous fuels in internal combustion engines introduce fuel upstream of the intake manifold. The intake manifolds that these engines possess, however, are too large to permit precise engine control using single point injection upstream of the manifold. With these engines, time lags occur in engine response and large fueling errors arise during transient engine operations. These engines, for example, often have limited space to accommodate multipoint injection hardware. Also, the costs to convert the existing intake manifold for multipoint injection may make alternative multipoint fuel injection impractical. These costs include, for example, tooling, machining, and labor costs for performing complicated installation and modification procedures for converting a conventional fuel engine to either a dedicated multipoint engine or a bi-fuel multipoint engine.
Other problems with conventional throttle-body alternative fuel systems adapted to internal combustion engines relate to the fact that their intake manifold has a larger volume than does the engine displacement volume. Because of these large manifolds, throttle-body (single point) gaseous fuel injection systems adapted these engines with large intake manifolds (1) inaccurately meter fuel; (2) have less than desirable driveability; and (3) produce higher than desirable emissions.